1. Field of the Invention
The invention relates in general to a control method and a system thereof, and more particularly to a method of calculating a demand threshold, and a method and a system of demand control.
2. Description of the Related Art
Although a convenient store only occupies small area, its energy consumption index is higher than that of a department store or a supermarket. As energy saving consciousness is getting higher, it is very important to design an effective and adequate energy saving system to control the electricity consumption of the convenient store.
The convenient store is the place to provide service for customers. While putting energy saving solutions into practice, it should be considered if the store operation is affected. In the store management system revealed in Japanese Patent No. JP2006178886, an integrated system combining a POS and a store management platform is provided. The system integrates remote access with energy saving countermeasures which controls electric equipment such as air conditioning and illuminating apparatus. However, the cost to set up these systems is too expensive, which results in a long period of time to recover the cost. Furthermore, the system is too complicated. As a result, the related hardware cost and the software design expense cannot be lowered, which significantly reduces the practicability.
Moreover, in the in-store equipment remote monitoring system revealed in US Patent No. 2002163431, a monitoring system is provided to collect the parameters such as indoor and outdoor illumination, the refrigerator temperature, outdoor temperature, the frequency of the automatic door, etc. The system predicts the next day's weather and brightness according to the historical information of the parameters, and calculates the suggested indoor illumination levels and temperature of air-conditioning with reference to the weather forecast. The user can manually adjust the operation of the equipment according to the suggested parameters. However, the cost to build up the system is too expensive. The system is complicated, which results in high related hardware cost and software design expense. The system cannot adjust the operation of the equipment automatically. When the environmental conditions change frequently and affect the decisions, the clerk has to take care of the customers and adjusts the equipment manually, which lowers the practicality greatly. Therefore, it is necessary to develop an automatic and effective energy saving strategy.
The electric fees of Taiwan Power Company include demand charge, energy charge and penalty charge. The store usually signs a contract with the power company to obtain electricity with lower rates. However, it s stipulated in the contract that the power consumption amount cannot exceed the contracted amount in each period of time in a month. For example, the power consumption amount cannot exceed 75 kWh for each 15 minutes. When the power consumption amount in any period of time segment exceeds the contracted amount, the store has to pay high penalty charge.
The average available power consumption is 5 kWh. However, when the power consumption within one minute is much higher than 5 kWh, it may result in the total power consumption of the time period exceeding 75 kWh even when the power consumption per minute of the following 14 minutes is lower than 5 kWh. The industrial customer found out that it is safer to set a threshold much lower than 5 kWh, such as 4 kWh. Therefore, the initial concept of demand control is derived accordingly. When the power consumption per minute is higher than 4 kWh, the power consumption has to be lowered.
However, the conventional method of demand control is manually setting a fixed amount to be the threshold. It is difficult to decide the amount, and the threshold cannot be adjusted according to practical conditions. When the threshold is too high, the power consumption may exceed the contracted amount, which results in high penalty charge. When the threshold is too low, the system sheds loads continuously, and the store cannot operate normally. Furthermore, even the business places of the same type may have different power consumption when the parameters, such as the location, the season, the number of customers and the floor area, are different. A fixed threshold cannot be applied to each store. When the threshold can not reflect the real timing to reduce power consumption, the following control process does not have much meaning.